In lighting industry, light-emitting diode (LED)-based light sources are attractive in use. As a novel and green light source, LEDs have lower power consumption, long life cycle, compact structure, and are environment-friendly, and thus are used in a wide range of fields such as sign indication, displaying, decoration, light source and urban night-lighting.
A LED is a solid semiconductor device with a fundamental structure typically having a frame, a semiconductor die arranged on the frame and packaging material for encapsulating the semiconductor die, such as Silica with phosphor powder and epoxy resin. The semiconductor die comprises a P-N junction where electrons will be driven toward a p-type region to recombine with electron holes, releasing energy in the form of photons. The optical wavelength is determined by the material constituting the P-N junction.
During operation in a LED, only a portion of electrical energy is converted into optical energy and the remaining is converted into heat, increasing LED temperature, which is the main factor for deterioration and failure. Therefore, it needs an optimized thermal design for LED lighting apparatus. Meanwhile, a LED driving power supply is usually integrated into the LED lighting apparatus and become an additional heat source. This makes the thermal design more difficult. On the other hand, the heat generated from LEDs may be transported to the LED driving power supply, shortening its life cycle and making its operational state unstable.